refactor(core): move background injection wiring from UI to backend

Wire ExecutionLifecycleService.setInjectionService() in Config constructor
so backgrounded executions inject directly via settleExecution instead of
routing through a useEffect bridge in AppContainer.

packages/cli/src/ui/AppContainer.tsx

@@ -85,8 +85,6 @@ import {
   buildUserSteeringHintPrompt,
   logBillingEvent,
   ApiKeyUpdatedEvent,
-  ExecutionLifecycleService,
-  type BackgroundCompletionInfo,
   type InjectionSource,
 } from '@google/gemini-cli-core';
 import { validateAuthMethod } from '../config/auth.js';
@@ -1119,28 +1117,6 @@ Logging in with Google... Restarting Gemini CLI to continue.
     };
   }, [config]);
 
-  // Wire background completion events from ExecutionLifecycleService into the
-  // injection service so completed backgrounded executions are reinjected.
-  useEffect(() => {
-    const bgListener = (info: BackgroundCompletionInfo) => {
-      // Use the execution creator's custom injection text if provided.
-      let text = info.injectionText;
-      if (text === null || text === undefined) {
-        // Fallback: generic format for executions without a custom formatter.
-        const header = info.error
-          ? `[Background execution (ID: ${info.executionId}) completed with error: ${info.error.message}]`
-          : `[Background execution (ID: ${info.executionId}) completed]`;
-        const body = info.output ? `\n${info.output}` : '';
-        text = `${header}${body}`;
-      }
-      config.injectionService.addInjection(text, 'background_completion');
-    };
-    ExecutionLifecycleService.onBackgroundComplete(bgListener);
-    return () => {
-      ExecutionLifecycleService.offBackgroundComplete(bgListener);
-    };
-  }, [config]);
-
   const {
     streamingState,
     submitQuery,

packages/core/src/config/config.ts

@@ -148,6 +148,7 @@ import type { AgentDefinition } from '../agents/types.js';
 import { fetchAdminControls } from '../code_assist/admin/admin_controls.js';
 import { isSubpath, resolveToRealPath } from '../utils/paths.js';
 import { InjectionService } from './injectionService.js';
+import { ExecutionLifecycleService } from '../services/executionLifecycleService.js';
 import { WORKSPACE_POLICY_TIER } from '../policy/config.js';
 import { loadPoliciesFromToml } from '../policy/toml-loader.js';
 
@@ -938,6 +939,7 @@ export class Config implements McpContext, AgentLoopContext {
     this.injectionService = new InjectionService(() =>
       this.isModelSteeringEnabled(),
     );
+    ExecutionLifecycleService.setInjectionService(this.injectionService);
     this.toolOutputMasking = {
       enabled: params.toolOutputMasking?.enabled ?? true,
       toolProtectionThreshold:

packages/core/src/services/executionLifecycleService.ts

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import type { InjectionService } from '../config/injectionService.js';
 import type { AnsiOutput } from '../utils/terminalSerializer.js';
 
 export type ExecutionMethod =
@@ -138,6 +139,15 @@ export class ExecutionLifecycleService {
   >();
   private static backgroundCompletionListeners =
     new Set<BackgroundCompletionListener>();
+  private static injectionService: InjectionService | null = null;
+
+  /**
+   * Wires a singleton InjectionService so that backgrounded executions
+   * can inject their output directly without routing through the UI layer.
+   */
+  static setInjectionService(service: InjectionService): void {
+    this.injectionService = service;
+  }
 
   /**
    * Registers a listener that fires when a previously-backgrounded
@@ -210,6 +220,7 @@ export class ExecutionLifecycleService {
     this.activeListeners.clear();
     this.exitedExecutionInfo.clear();
     this.backgroundCompletionListeners.clear();
+    this.injectionService = null;
     this.nextExecutionId = NON_PROCESS_EXECUTION_ID_START;
   }
 
@@ -323,6 +334,16 @@ export class ExecutionLifecycleService {
         error: result.error,
         injectionText,
       };
+
+      // Inject directly into the model conversation if injection text is
+      // available and the injection service has been wired up.
+      if (injectionText && this.injectionService) {
+        this.injectionService.addInjection(
+          injectionText,
+          'background_completion',
+        );
+      }
+
       for (const listener of this.backgroundCompletionListeners) {
         listener(info);
       }